grams = molecular weight × moles
= 80 g/mole × 0.05 moles
= 4 grams or 4,000 mg (choice (D))
- B This is another math problem, but this one involves the ideal gas law. A
couple of things first: 1) Since we don’t have a calculator, let’s round off
the value of R to 0.1 L•atm/mol•K, and 2) remember that T must be in K,
not °C, for PV = nRT to work correctly. So
PV = nRT or V = nRT/P
= (0.5 moles × 0.1 L•atm/mol•K × 300 K)/3
atm
= (15 L•atm)/3 atm
= 5 (choice (B))
- E For covalent compounds, a di- prefix signifies two, and the tetra- prefix
signifies four.
- E Recall that when ΔG is negative, a reaction is spontaneous, and when
ΔG is positive, a reaction is nonspontaneous. The question indicates that
the reaction in question is endothermic—i.e., ΔH is positive. Looking at
the equation provided, the effect that decreasing T has will depend on the
sign of ΔS. But the question doesn’t tell us the sign of ΔS, nor can we
figure it out on our own. Therefore, there is no way to make any
conclusions—choice (E).
- B First ionization energy is a periodic trend that increases up and to the
right on the periodic table. After looking at the position of these elements
on the periodic table, carbon is clearly the best answer—choice (B).
- D Hydrogen bonding is the strongest type of intermolecular force. Other
types of permanent dipoles would be next strongest, and the temporary
dipoles created through London dispersion forces would be the weakest
type of intermolecular force.
